1. Field of the Invention
The present invention relates to a fuel cell formed by stacking electrolyte electrode assemblies between separators. Each of the electrolyte electrode assemblies includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. Further, the present invention relates to a fuel cell stack formed by stacking a plurality of the fuel cells.
2. Description of the Related Art
Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, generally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
In the fuel cell, in order to supply a fuel gas such as a hydrogen-containing gas and an oxygen-containing gas such as the air to the anode and the cathode of the electrolyte electrode assembly, a fuel gas channel and an oxygen-containing gas channel are formed along surfaces of the separator. The fuel cell stack may adopt internal manifold structure where a fuel gas supply unit and an oxygen-containing gas supply unit extend in the stacking direction for distributing the fuel gas and the oxygen-containing gas to each fuel gas channel and each oxygen-containing gas channel.
For example, in a flat plate type solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-172594, unit cells (not shown) and separators 1 are provided alternately, and as shown in FIG. 18, gas supply holes 2a, 3a, and gas discharge holes 2b, 3b extend through four corners of the separator 1 in the stacking direction, and a plurality of gas flow grooves 4a and ridges 4b in a plurality of rows are arranged alternately along the surface of the separator 1.
The gas flow grooves 4a are connected to the gas supply hole 2a and the gas discharge hole 2b through triangular recesses 5a, 5b. A throttle section 6 and blocks 7 are provided in a gas inlet of the triangular recess 5a, near the gas supply hole 2a, as means for limiting the flow rate of the gas. The throttle section 6 and the blocks 7 function to increase the pressure loss of the gas flowing from the gas supply hole 2a to the gas inlet section.
Further, at opposite ends of the gas flow grooves 4a, a shallow gas flow inlet 8a and a shallow gas flow outlet 8b are provided for pressure loss function of the gas flow.
However, in the conventional technique, in order to suitably achieve the pressure loss in the gas which flows from the gas supply hole 2a to the gas inlet section, the throttle section 6 and the blocks 7 need to be fabricated with a high degree of accuracy. Therefore, the production cost of the separator 1 is significantly high uneconomically.
Further, since a single electrolyte electrode assembly (MEA) is provided in each space between the adjacent separators 1. The reactant gases are not supplied to the electrolyte electrode assemblies under the same condition, and it is difficult to supply the reactant gases equally to each of the electrolyte electrode assemblies. As a result, the desired power generation performance cannot be achieved in the fuel cell stack as a whole.